1898.] NATURAL SCIENCES OF PHILADELPHIA. 363 



nasal bones form about 33.3 percent of the occipitonasal length, 

 while in E. rutilus they form about 28.5 percent only. The differ- 

 ence is due to the less backward extent of the nasals in E. rutilus, 

 rather than to any actual shortening of the rostrum. Audital bulla? 

 large and rounded as in E. alascensis, very different from those of 

 E. ivosnessenskii. 



Measurements of an adult skull from Lapland : greatest length, 

 24 mm. ; basal length, 22.4 ; basilar length, 20.6 ; zygomatic breadth, 

 13; mastoid breadth, 11.8 ; interorbital constriction, 4 ; nasals, 7; 

 incisive foramen, 5 ; diastema, 7.4 ; maxillary molar series (alve- 

 oli), 5 ; mandible, 13.8 ; mandibular molar series (alveoli), 5. 



Teeth. — The teeth of Evotomys rutilus (fig. 2 a) do not differ ap- 

 preciably from those of E. ivosnessenskii and E. alascensis. 



Ears, feet and tail. — So far as can be judged from dry skins the 

 ears of Evotomys rutilus do not differ appreciably in form from those 

 of E. alascensis and E. ivosnessenskii. They are, however, ap- 

 parently a trifle larger than in the latter. Feet broad, as in the 

 Alaskan form. Tail about as in E. alascensis, but considerably 

 longer and somewhat less densely haired. 



Color. — An adult male from northern Sweden taken in December 

 and another specimen from same region but without date, agree 

 very closely in color. Both have the dorsal stripe a clear bright 

 chestnut, faintly darkened by a slight admixture of black-tipped 

 hairs. The sides are ochraceous-buff, and the belly dirty white or 

 cream color. Feet whitish ; ears chestnut. Tail sharply bicolor, 

 brownish, tinged with red above, dirty white below. Fur every- 

 where slaty plumbeous at base, this color appearing irregularly at 

 surface on belly and sides. Two other undated skins from Lap- 

 land are slightly paler in color. 



Measurements. — For measurements of Evotomys rutilus see table, 

 page 366. 



Specimens examined. — Four, from the following localities : 



Lapland : no definite locality, 2. 



Sweden : Karesnaudo, 1 ; no definite locality (northern Sweden), 1. 



General remarks. — The Arctic red-backed mouse of northern 

 Europe is readily distinguishable among the known Arctic forms* 



4 There are no less than five of these, E. rutilus, E. wosnessensldi, E. alas- 

 censis, E. ungava, and E. proteus. For descriptions of the last two, both of 

 which are from Labrador, see Bailey, Proc. Biolog. Soc. Washington, XI, 

 pp. 130, 131, and 137, May 13, 1897. 



